1. Field of the Invention
The present invention generally relates to an automatic power transmission of an automotive vehicle and, more particularly, relates to a gear speed range shift control apparatus of the automatic power transmission used together with a device which prevents a friction generated on a one way clutch installed in a power transmission train of the automatic power transmission.
2. Description of the Background Art
An automatic power transmission selects one of gear shift speed ranges according to a selective hydraulic (working pressure) operation (engagement) of various types of frictional elements (frictional clutch and/or frictional brakes) and performs a gear shifting of the present gear shift speed range to the other gear shift range according to a change of the operating frictional elements.
When an up-shifting of the gear speed range from a low gear speed range to a high gear speed range occurs, a power transmission at the low gear speed range is carried out via a one way clutch so that the up-shifting of the gear speed range to the high gear speed range is completed through of an overrun of the one way clutch. At this time, the overrun of the one way clutch is preferable as a countermeasure against an occurrence of a gear shift shock. Currently, many automatic power transmissions have adopted this countermeasure.
A Japanese Service Manual titled "NISSAN MAXIMA NEW MODEL EXPLANATION BOOK J30 TYPE SERIES, INTRODUCTION OF VEHICLE MODIFIED POINTS" published in August, 1991 exemplifies the above-described automatic transmission.
In the disclosed Japanese Service Manual identified above, the automatic transmission includes a forward one way clutch corresponding to the one way clutch described above, the forward one way clutch being engaged so as to contribute to the power transmission at the time of the gear speed ranges from a 1st speed range to a 3rd speed range and being in an overrun state at the time when the gear shift occurs to the fourth (4th) speed range, the gear shifting to the 4th speed range being carried out with a band brake additionally operated in the 3rd speed range selected state so that the gear range shift can smoothly be executed.
However, since, at the 4-th gear speed range, outer and inner laces of the forward one-way clutch are left coupled to separate rotation members, respectively, the rotation members being independently and separately rotated, a friction of the one way clutch involved with the relative rotations between the outer and inner laces cannot be avoided and can cause an increased power loss, thus introducing a wasteful fuel consumption of the associated engine.